1. Field of the Invention
The present invention relates to a laptop or notebook type portable personal computer system and, more particularly, to a computer system for interfacing different programs.
2. Description of the Related Art
In recent years, high-performance microprocessors have been developed with the advance of semiconductor techniques. A high-performance microprocessor is used as a CPU for a laptop or notebook type portable personal computer system.
Typical examples of such a CPU are Intel386 and Intel486 CPUs available from Intel, U.S.A. Such a CPU has two operating modes called a real mode and a protect mode. The real and protect modes employ different memory addressing schemes. In the real mode, the maximum accessible memory space is a 1-Mbyte area. In the protect mode, a maximum of 4-Gbyte memory area per task is accessible.
Operating systems executed by personal computer systems have been recently developed, and an operating system supporting a multitask function is gradually used. Most of such high-performance operating systems are configured to operate in the protect mode.
In a personal computer, a program called a system BIOS (Basic I/O System) for only hardware access is used to set hardware and the operating system in the system independent of each other and release the operating system from hardware access control. This system BIOS includes a plurality of function execution routines for hardware access. These function execution routines provide functions of performing various hardware access operations to the operating system.
The function execution routines of the system BIOS are realized by CPU software interrupt instructions (INT instructions). For this reason, the operating system calls a desired function execution function in accordance with an INT instruction to perform necessary hardware control.
However, all the system BIOS function execution routines are designed to be operated in the real mode because the system BIOS is arranged on an assumption that an operating system is executed in the real mode.
For this reason, the following operation must be performed. In an operating system environment set in the protect mode, as shown in FIG. 1, after the CPU operating mode is temporarily changed from the protect mode to the real mode, an INT instruction is executed to call a corresponding function execution routine. When this function execution routine is completed to cause the control to return to the main routine, the protect mode must be changed to the real mode again.
For this reason, when an operating system operating in the protect mode is used, a routine for changing the CPU operating mode and a routine for calling the function execution routine of the system BIOS in accordance with the INT instruction must be built into the BIOS interface portion of the operating system, thereby undesirably complicating coding.
In a conventional case, the routine for changing the CPU operating mode must be built into the BIOS interface portion such as an operating system operating in the protect mode, thereby undesirably complicating coding.